Section 1
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Last updated
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Date created
Mar 1, 2020
Cards (62)
Section 1
(50 cards)
exception
a detected runtime error that commonly prints an error message and terminates the program.
A programmer compares strings relationally
notation str1.compareTo(str2). compareTo() returns values as follows. str1 less-than str2 — Negative number — str1.compareTo(str2) < 0
how to make a random number
uses randGen.nextInt(6) to get a new random number between 0 and 5
floating-point literal
a number with a fractional part, even if that fraction is 0, as in 1.0, 0.0, or 99.573. Good practice is to always have a digit before the decimal point, as in 0.5.
index
string character has a position number — he numbering starts with 0, not 1. charAt(): The notation someString.charAt(0)
What is bigger 'A' or 'a'?
'A' is 65, B' is 66, etc., while 'a' is 97, 'b' is 98, etc.
someString.charAt(0)
determines the character at index 0
logic error
while a program runs, also called a runtime error or bug
Scanner
first creating a Scanner object via the statement Scanner scnr = new Scanner(System.in) — System.in corresponds to keyboard input — read using hourlyWage = scnr.nextInt()
memory
a circuit that can store 0s and 1s in each of a series of thousands of addressed locations
final variable
A constant — ex/ final double SPEED_OF_SOUND = 761.207;
length()
number of character
isEmpty()
true if length is 0
bytecode / virtual machine
allows the same executable to run on different processor types so portable
concat(moreString)
Creates a new String that appends the String moreString at the end.
For an arithmetic operator like + or *, if either operand is a double
the other is automatically converted to double, and then a floating-point operation is performed.
System.out.print vs System.out.println
(note the ln at the end, short for "line"), starts a new line after the printed output. *(Text in double quotes " " is known as a string literal)
floating-point types should not be compared using the...
equality operators, due to the imprecise representation of floating-point numbers
compiler
tool that converts a program into low-level machine instructions (0s and 1s)
Import statement.
import packageName.ClassName;
syntax error
violate a programming language's rules on how symbols can be combined to create a program. Ex: forgot a ;
statement
is a program instruction. Each statement usually appears on its own line. Each program statement ends with a semicolon ";", like each English sentence ends with a period.
A programmer can compare two strings using
str1.equals(str2). The equals method returns true if the two strings are equal
declare a boolean—write code
boolean isNeg = false;
How to solve problems
I SEE — Identify - Set Up - Execute - Evaluate
indexOf(item)
Index of first item occurrence, else -1. (finds the #occurance of item. lastIndexOf(item) finds the last occurrence .
Definding a string
String wordRelative = ""; — note the capital S
bitwise
logical AND is && and not just &, and likewise that logical OR is || and not just | — When both operands are integers, the bitwise operators evaluate to an integer value
compile-time error
syntax error is detected by the compiler
Not finding an error at the specified line...
the programmer should look to previous lines. Ex/ ; error but actually a () error
branching
execute either one statement group or another, depending on an expression's value. An example is to print "Too young to drive" if userAge < 16, else print "OK to drive"
memory
is composed of numerous individual locations, each able to store a value. The statement (veriable) int wage = 20 reserves a location in memory
Oerflow
when the value being assigned to a variable is greater than the maximum value the variable can store. Overflow with floating-point results in infinity.
System.out.println("Wage is: " + wage) output
Wage is: 20
programs called assemblers
translate human readable instructions, such as "Mul 97, #9, 98", known as assembly language instructions, into machine instructions
substring(startIndex, endIndex)
Returns substring starting at startIndex and ending at endIndex - 1. length is endIndex-startIndex
circuits called processors
to process (aka execute) a list of desired calculations, each calculation called instruction
isNeg = (userNum < 0);
Alternative way to set a Boolean variable
To print multiple character variables
input should start with "" + and each character variable should be separated by a +
import java.util.Scanner;
Enabling reading of input.
Assignment statement
variableName = expression;
can compare strings while ignoring case using
str1.equalsIgnoreCase(str2) and str1.compareToIgnoreCase(str2)
System.out.println(songNum " songs"); — what is the error
"+"
1 / 2 is what—(5 + 10 + 15) * (1 / 3) is what
Zero 0
scnr.next() versus scnr.nextInt()
The first one gets a string while the other gets a nu mber — scnr.nextLine() read all until ENTER key
dimentially consistence
allways check dimentions
method
a list of statements that can be executed by referring to the method's name — Invoking a method is a method call
6.02e+23 is what
represent 6.02x1023
pseudo-random number generator
produces a specific sequence of numbers based on a seed number
warning like "Warning, dividing by 0 is not defined"
doesn't stop the compiler from creating an executable program, but indicates a possible logic error.
Section 2
(12 cards)